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"Black anodize turning purple"


I read an earlier posting where the black dye was turning purple over time. My products are having similar problems.
Since I am not the anodizer, are there any other factors, i.e., problems with the base material, that could cause a similar reaction?

Dennis Jolley
MarathonNorco Aerospace, Inc. - Waco, Texas


There are over 36,000 letters on this site which means that we don't always know which letter you are referring to. In this case it probably would be either letter 12348 or 31658. So a good first thing to do to get some additional ideas would be to read whichever of those two letters your didn't :-)

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


What alloy are you using? I have had a similar experience with cast aluminum tooling plate (Mic-6). After talking to the anodizer we came to the conclusion that they were not leaving the part in the neutralizing bath long enough before the dyeing process. This caused the acid to leach out over time and effect the color of the dye which turned from black to purple.

Bryan Parker
- New Mexico


The letter was number 12348.

The alloys I am referencing are 2024 and 6061.

I have had feedback from a metallurgist that the anodize could be improperly sealed allowing the dye to fade.

Dennis Jolley
- Waco, Texas


I have had the same problem with parts dyed black. Black anodizing require a lot more coating thickness to be able to get the black dye to be dark enough. The coating thickness is thicker,so the seal time must be a lot longer. If normal seal time is 5 minutes back dye seal time should be at least 15 minutes.

Raymond Hendrix Troy, Tennessee


Anodize does not have to be thicker for black if you run your dye at full concentration. We use black hbl which is rated best for light fastness, also an improper seal will do the same thing. I receive a lot of parts in my shop to strip and replate due to the same problem.

Steve Tanner
Micron Industries, Dallas Precious Metals - Garland, Texas, USA

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